This invention relates to a system for deicing aircraft and more particularly to a glycol/air coaxial stream deicing system wherein glycol and forced air are applied as a glycol stream within a forced air stream. The stream is charged to hydrodynamically dislodge and remove ice or other frozen deposits from surfaces such as aircraft.
As used herein, the terms xe2x80x9cglycol,xe2x80x9d xe2x80x9cdeicing fluid,xe2x80x9d and xe2x80x9cType 1 fluidxe2x80x9d are used interchangeably to mean Type 1 deicing fluidxe2x80x94a mixture of glycol (ethylene or propylene) and water. This is distinct from Type II, III or IV xe2x80x9canti-icingxe2x80x9d fluids used to prevent the accumulation of frozen precipitation on aircraft surfaces that have been previously de-iced.
Ground deicing of aircraft is an important step in preparing aircraft for safe flight during snow, ice and frost weather conditions. Accumulation of these winter products on aircraft surfaces (e.g., wings, tail and rudder) disturbs the aerodynamic performance of these surfaces creating unstable flight conditions and this has caused aircraft to crash.
Conventional aircraft deicing systems consist of ground or truck mounted spray systems that apply hot (typically about 180xc2x0 F.) deicing fluid at rates varying from 35 gallons per minute (gpm) to 100 gpm to the aircraft surfaces. The most common spray nozzle is the same type used by firefighters. This nozzle (e.g., Task Force Tip) can spray a solid jet from 1 to 2 inches in diameter or be adjusted to a very wide conical spray pattern. Conventional deicing thermally removes snow and ice by melting it away and augmented, to some extent, by the hydrodynamic sweeping action of the deicing jet. This deicing process is effective but often very large amounts of deicing fluid are used, particularly if there is much accumulation of wet snow or the snow and ice are frozen to the aircraft surfaces. Since glycol is expensive and toxic, conventional deicing creates significant economic and waste management problems for airline and airport operators.
Various deicing systems using little or no glycol have been tried and, to date, these systems have demonstrated limited effectiveness. Therefore, they have not gained acceptance by commercial deicing operators. A common approach for deicing aircraft while reducing glycol usage is to use a combination of forced air and conventional deicing systems. Such systems have been used by the U.S. Air Force for decades. The Air Force is using what they call xe2x80x9chot blastxe2x80x9d deicing trucks at various bases such as Elmendorf AFB in Alaska. The xe2x80x9chot blastxe2x80x9d deicer has an auxiliary power unit (APU) which produces about 35 pounds per square inch (psi) of air at a flow rate of 100 pounds per minute (ppm). This air is delivered to a dedicated air nozzle to first flow away the loose snow and ice. The conventional system is then turned on to finish the job in this 2-step process.
The xe2x80x9chot blastxe2x80x9d deicer saves glycol but it significantly extends the deicing cycle time because it is a 2-step process. This is very undesirable for commercial deicers where tight schedules must be maintained. Furthermore, under severe deicing conditions, when air alone is not very effective, the glycol savings are minimal because the conventional process becomes the primary method of deicing.
Some of the patents covering conventional deicing and its refinements include U.S. Pat. Nos. 3,243,123; 4,073, 4,826,107; and 5,028,017. Other publications describe various deicing systems, (some of which are believed to have been tested) to improve the deicing process, either by reducing or eliminating the use of glycol, or by applying glycol in a more efficient manner such that the glycol usage is reduced. These include, for instance, U.S. Pat. Nos. 5,244,168 and 5,104,068.
Deicing fluid entrained in air has been know for a number of years, as shown for instance in U.S. Pat. Nos. 2,482,720 and 2,406,473. In U.S. Pat. No. 5,244,168, a xe2x80x9cwell-dispersed atomized spray patternxe2x80x9d (col. 7, line 35) or a xe2x80x9cspray pattern of a high speed colloidal suspension of deicing fluid in airxe2x80x9d (claim 1, lines 21-22) is produced. In this latter patent, the glycol mixes and atomizes in the air stream. The energy transfer process associated with the mixing and atomizing reduces the kinetic energy of the air stream which, in turn, reduces the effectiveness of the air stream/glycol mixture to dislodge snow and ice that is frozen to or adhered to an aircraft. Thus, this atomization process reduces the effectiveness of the air stream in breaking loose snow and ice that is frozen to or adhered to an aircraft surface and also reduces the effectiveness of the air stream in moving heavy, wet snow. In addition, the mixture of atomized glycol and high velocity air adds more wetness to the snow further inhibiting the removal of wet snow.
Another novel deicing technique developed by InfraTek Radiant Energy Corporation uses gas-fired infra-red heaters built into the interior structure of a large prefab type hangar to melt ice from the aircraft surfaces. Two fundamental problems have surfaced with this deicing process. First, the frequency of the infra red heaters is such that snow melts slowly, extending the deicing cycle time. Second, testing shows that melting ice from the upper surfaces of the aircraft often re-freezes on the lower surfaces not exposed to the infra-red rays.
U.S. Pat. No. 5,104,068 describes an apparatus for both de-icing and anti-icing an aircraft in one xe2x80x9cpass.xe2x80x9d The apparatus consists of articulated booms on each side of the aircraft to be processed. These booms extend over the entire length of each wing and each has two series of nozzles. One set is for dispensing a deicing fluid mixture and the other set is for dispensing anti-icing fluid. There is also a set of booms underneath the aircraft for processing the lower aircraft surfaces. The patent also describes the use of different mixtures of pressurized air, water and glycol (Type I) with the mixture varied in accordance with the particular weather conditions. The apparatus and process described above are commercially known by the name xe2x80x9cWhisper Wash.xe2x80x9d Benefits expected to be realized presumably include reduced glycol usage and reduced de-ice/anti-ice cycle time.
The present invention overcomes disadvantages of the prior systems and provides a new hybrid deicing system that produces an independent, high velocity stream of deicing fluid that is encased by an independent stream of air at a substantially equal velocity for efficient and effective removal of ice from a surface. This invention (xe2x80x9chybrid deicingxe2x80x9d), utilizing two fluid flow technologies and a unique coaxial nozzle, yields an efficient, stand-alone deicing system, i.e. a complete deicing system that reduces glycol usage and deicing cycle time. Laboratory tests have validated that xe2x80x9chybrid deicingxe2x80x9d can quickly and safely remove snow and ice frozen to a simulated aircraft surface. These tests also indicate that deicing glycol usage can be reduced to 10% or less relative to conventional usage, thereby providing the deicing operator with significant economic and waste management benefits. It is estimated that hybrid deicing will reduce conventional deicing cycle time, in many deicing situations, by 10% or more providing an additional benefit to the operator.
In the present invention, an essentially independent stream within an essentially independent stream provides a deicing fluid (such as a glycol/water mixture) entrained within and encased by a surrounding jacket of entraining fluid (such as air). Also provided is a coaxial nozzle assembly that produces two essentially independent streams of Type I glycol fluid and air. Both streams exit the nozzle assembly at substantially equal velocities and, preferably, at or above sonic velocity such as about 600-800 mph. The precise velocity of the streams depends on the upstream pressures and temperatures of the fluids.
This combination of a high velocity coaxial stream within a stream hydrodynamically and thermally removes adhered ice, freezing rain, and snow (light, wet or heavy). Further, the surrounding sheath or stream of forced air reduces the fluid energy and momentum loss of the inner stream of deicing fluid, thereby increasing the effective snow/ice removal range (i.e., distance from the nozzle exit) of the combined streams. This invention will de-ice aircraft and other surfaces as effectively as the conventional hot glycol wash method but with glycol application rates reduced to 10% or less of conventional rates. Consequently, the present invention significantly reduces deicing costs and the impact on the environment.